Systems and methods for motion compensation in ultrasonic respiration monitoring

ABSTRACT

Described herein are example methods, devices and systems for motion compensation in ultrasonic respiration monitoring. A respiration detection system includes a first probe placed on a front side of a patient&#39;s body and a second probe placed on a dorsal side of the body. The first probe includes an ultrasound transducer, a first accelerometer unit and a magnetic field sensor unit, and the second probe includes a second accelerometer unit and magnetic field sensor unit. Due to respiration of the patient, the abdominal region of the body moves, creating measurement errors when an ultrasound beam is directed towards an internal structure (internal tissue region) inside the patient&#39;s body. Correction for such measurement errors uses input data from the first and second accelerometer units and the magnetic field sensor unit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.16/216,632, filed on Dec. 11, 2018, now U.S. Pat. No. 10,398,351, whichis incorporated herein by reference in its entirety.

BACKGROUND Field

The present disclosure relates to methods, devices and systems formotion compensation in ultrasonic respiration monitoring of patients,including correcting for measurement errors resulting from movements ofthe abdominal region during respiration.

Background

Measurement and monitoring of respiration is important for treatment ofa wide range of medical conditions in patients. The thoracic diaphragmis the main breathing muscle, and its dysfunction can be symptomatic ofmany respiratory disorders and conditions.

In order to monitor respiration, various ultrasonic transducer deviceprobes have been utilized. For example, an ultrasonic transducer devicemay be located in a housing of a probe and embedded therein by anultrasound sonolucent material, such as a silicone rubber material oranother material that allows passage of ultrasonic waves. The ultrasonictransducer probe may be placed on the skin surface of a patient's bodyusing a double-sided tacky tape having a reinforcing web between its twotacky layers.

While such probes may be useful in monitoring respiration properties ofa patient, it is important to take into consideration correction oferror signals caused by movement of the probe on the front surface ofthe patient during respiration. For example, the abdominal region of thebody moves as the patient breathes, which causes the probe to move. Insome cases, the magnitude of such error signals may be significant tomeasurement reliability.

SUMMARY

The present disclosure relates to systems and methods for correctingmeasurement errors during ultrasonic respiration monitoring, in whichthe measurement errors result from abdominal movements in a patient'sbody during breathing. Embodiments of the invention detect motion ofvarious tissues and structures in the body including, for example, thespleen, liver, or a kidney. But, for purposes of illustrating theprinciples of embodiment of the invention, the following discussionsprimarily focus on motion detection of the liver. For example, whencomparing measurements made with an abdominal probe attached to thefront side of the human body and moving with the abdominal wall, liverexcursion appears to be about 30 to 40% less than when measuring with amechanically fixed probe.

These measurement errors are caused by respiratory motion imposed ontothe probe, counteracting the echo distance variations along thedirection of the ultrasound beam. Such errors may present a risk toevaluation certainty of the respiration modes and parameters ofpatients, particularly for a patient with a respiration issue of medicalconcern. Thus, the aspects of the present disclosure relate toeffectively compensating for such highly unwanted errors and providinghigher accuracy in respiration monitoring.

In an embodiment, a respiration detection system includes a first probeand a second probe. The first probe is configured to be placed on afront side of the body of a patient, and the second probe is configuredto be placed on a dorsal side of the body. The first probe includes anultrasonic transducer, a first accelerometer unit, and a first magneticfield unit, in which the ultrasonic transducer, the first accelerometerunit, and the first magnetic field unit are stationary located in thefirst probe. The ultrasonic transducer is stationary located within thefirst probe and has a transceiving face oriented at an acute anglerelative to a front plane of the first probe. The ultrasonic transduceris configured to produce an ultrasound beam at the transceiving face fortransmission into an internal structure inside the body of the patient.The second probe includes a second accelerometer unit and a secondmagnetic field unit, in which the second accelerometer unit and thesecond magnetic field unit are stationary located in the second probe.The ultrasonic transducer, the first and second accelerometer units, andthe first and second magnetic field units are coupled to a signalprocessor.

In another embodiment, a method for motion compensation inultrasound-based detection of respiration parameters of a patient isdisclosed. The method includes attaching a first probe to a front bodysurface of the patient, the first probe having an ultrasound transducer,a first accelerometer unit, and a first magnetic field unit, attaching asecond probe to a dorsal body surface of the patient, the second probehaving a second accelerometer unit, and a second magnetic field unit,and providing a signal processor coupled to the ultrasonic transducer,the first and second accelerometer units, and the first and secondmagnetic field units. The method further includes transmitting, from theultrasound transducer in the first probe, an ultrasound beam into aninternal structure inside the body of the patient, receiving, at theultrasonic transducer in the first probe, ultrasound echo signals fromthe internal structure, generating, by the second magnetic field unit, amagnetic field transmitted to and detected by the first magnetic fieldunit, and calculating, using the signal processor, an orientation of thefirst accelerometer unit relative to a fixed coordinate frame usingderived parameters from the first accelerometer unit, and furthercalculating the derived parameters as unit vectors representing anorientation of the ultrasound beam and an orientation of the firstmagnetic field unit. Additionally, the method includes calculating,using the signal processor, an orientation of the second accelerometerunit relative to a fixed coordinate frame using further derivedparameters, and calculating the further derived parameters includingbody back support tilt angle (a) and unit vectors representative of aspatial direction from the second magnetic field unit to the firstmagnetic field unit, an orientation of the second magnetic field unit,and an expected direction of motion of the internal structure duringexhalation, calculating, using the signal processor, any varyingdistance between the first and second magnetic field units based on thedetection of the magnetic field, and processing, using the signalprocessor, results from the calculated orientations, derived parametersfrom the first and second accelerometer units, and the varying distanceto generate correction parameters to compensate for measurement errorsin received ultrasound echo signals.

Further features and advantages, as well as the structure and operationof various embodiments, are described in detail below with reference tothe accompanying drawings. It is noted that the specific embodimentsdescribed herein are not intended to be limiting. Such embodiments arepresented herein for illustrative purposes only. Additional embodimentswill be apparent to persons skilled in the relevant art(s) based on theteachings contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate embodiments of the present inventionand, together with the description, further serve to explain theprinciples of the invention and to enable a person skilled in thepertinent art to make and use the invention.

FIGS. 1A-1C illustrate example diagrams of a human torso showingultrasonic transducer device placement, according to embodiments of thepresent disclosure.

FIGS. 2A and 2B illustrate example diagrams of probe locations on thehuman body for motion detection of the liver, spleen, or kidney,according to embodiments of the present disclosure.

FIG. 3 illustrates a rear perspective view of a front ultrasonictransducer device probe, according to embodiments of the presentdisclosure.

FIG. 4 illustrates a rear plan view of the probe of FIG. 3, according toembodiments of the present disclosure.

FIG. 5 illustrates a cross-section of a first embodiment of the frontultrasonic transducer device probe, according to embodiments of thepresent disclosure.

FIG. 6 illustrates a cross-section of a second embodiment of the frontultrasonic transducer device probe, according to embodiments of thepresent disclosure.

FIG. 7 illustrates a cross-section of a third embodiment of the frontultrasonic transducer device probe, according to embodiments of thepresent disclosure.

FIG. 8 illustrates a cross-section of a fourth embodiment of the frontultrasonic transducer device probe, according to embodiments of thepresent disclosure.

FIG. 9 illustrates a cross-section of a fifth embodiment of the frontultrasonic transducer device probe, according to embodiments of thepresent disclosure.

FIG. 10 illustrates a cross-section of a sixth embodiment of the frontultrasonic transducer device probe, according to embodiments of thepresent disclosure.

FIG. 11 illustrates a cross-section of a seventh embodiment of the frontultrasonic transducer device probe, according to embodiments of thepresent disclosure.

FIG. 12 illustrates a cross-section of an eight embodiment of the frontultrasonic transducer device probe, according to embodiments of thepresent disclosure.

FIG. 13 illustrates a perspective, front full view of the probe of FIGS.9 and 10, prior to installation of first and second materials in theprobe, according to embodiments of the present disclosure.

FIG. 14 illustrates another perspective, front full view of the probe ofFIG. 13 from a different angle, according to embodiments of the presentdisclosure.

FIG. 15 illustrates a perspective, front sectioned view of the probe ofFIGS. 13 and 14, according to embodiments of the present disclosure.

FIG. 16 illustrates a perspective rear view of a rear probe to be placedon the dorsal side of the human body and interface with the front probeon the front side of the human body, according to embodiments of thepresent disclosure.

FIG. 17 illustrates a perspective, front full view of the probe of FIG.16, prior to installation of a fourth material and optional applicationof a tacky body, according to embodiments of the present disclosure.

FIG. 18 illustrates a perspective, front sectioned view of the probe ofFIG. 17, according to embodiments of the present disclosure.

FIG. 19 illustrates a cross-section of the rear probe beforeinstallation of the fourth material, according to embodiments of thepresent disclosure.

FIG. 20 illustrates a sectional view of FIG. 19 after installation ofthe fourth material, according to embodiments of the present disclosure.

FIG. 21 illustrates a sectional view of FIG. 20 after addition of atacky body of a fifth material, an adhesive member, or a double-sidedtacky tape material, according to embodiments of the present disclosure.

FIG. 22 illustrates a simplified block schematic diagram of anembodiment of the inventive system for performing signal processingrelated to range calculation and motion compensation, according toembodiments of the present disclosure.

FIG. 23 illustrates a cross-section diagram showing basic principles forrespiration detection using ultrasound beam directed at a human liver,according to embodiments of the present disclosure.

FIG. 24 illustrates a cross-section diagram showing motion of a chestand abdominal region of the human body during respiration, according toembodiments of the present disclosure.

FIG. 25 illustrates a cross-section diagram showing effects of abdominalshape changes during respiration, according to embodiments of thepresent disclosure.

FIG. 26 illustrates a cross-section diagram showing rear (ancillary)sensor probe placement, as also shown in FIG. 1A, 1B, 2A or 2B,according to embodiments of the present disclosure.

FIG. 27 illustrates a schematic diagram showing derivation of signalsfrom accelerometers in the front and rear probes, according toembodiments of the present disclosure.

FIG. 28 illustrates a schematic diagram showing signal processingrelated to range calculation and motion compensation, according toembodiments of the present disclosure.

FIG. 29 illustrates an example graph showing first rotation (p) seenfrom the positive x-axis, according to embodiments of the presentdisclosure.

FIG. 30 illustrates an example graph showing orientation of the gravityvector prior to a second rotation as seen from the positive y-axis,according to embodiments of the present disclosure.

FIG. 31 illustrates an example graph showing probe coordinates andmeasured acceleration seen from the positive y-axis, according toembodiments of the present disclosure.

FIG. 32 illustrates an example graph showing a situation after the firstrotation seen from the global positive x-axis, according to embodimentsof the present disclosure.

FIG. 33 illustrates direction of the measured acceleration vector afterthe second rotation, according to embodiments of the present disclosure.

FIG. 34 illustrates a calibration setup, according to embodiments of thepresent disclosure.

Embodiments of the present invention will be described with reference tothe accompanying drawings.

DETAILED DESCRIPTION

The following Detailed Description refers to accompanying drawings toillustrate exemplary embodiments consistent with the disclosure.References in the Detailed Description to “one exemplary embodiment,”“an exemplary embodiment,” “an example exemplary embodiment,” etc.,indicate that the exemplary embodiment described may include aparticular feature, structure, or characteristic, but every exemplaryembodiment might not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same exemplary embodiment. Further, when a particularfeature, structure, or characteristic is described in connection with anexemplary embodiment, it is within the knowledge of those skilled in therelevant art(s) to affect such feature, structure, or characteristic inconnection with other exemplary embodiments whether or not explicitlydescribed.

The exemplary embodiments described herein are provided for illustrativepurposes, and are not limiting. Other exemplary embodiments arepossible, and modifications may be made to the exemplary embodimentswithin the spirit and scope of the disclosure. Therefore, the DetailedDescription is not meant to limit the invention. Rather, the scope ofthe invention is defined only in accordance with the following claimsand their equivalents.

Embodiments may be implemented in hardware (e.g., circuits), firmware,software, or any combination thereof. Embodiments may also beimplemented as instructions stored on a machine-readable medium, whichmay be read and executed by one or more processors. A machine-readablemedium may include any mechanism for storing or transmitting informationin a form readable by a machine (e.g., a computing device). For example,a machine-readable medium may include read only memory (ROM); randomaccess memory (RAM); magnetic disk storage media; optical storage media;flash memory devices; electrical, optical, acoustical or other forms ofpropagated signals (e.g., carrier waves, infrared signals, digitalsignals, etc.), and others. Further, firmware, software, routines,instructions may be described herein as performing certain actions.However, it should be appreciated that such descriptions are merely forconvenience and that such actions in fact result from computing devices,processors, controllers, or other devices executing the firmware,software, routines, instructions, etc. Further, any of theimplementation variations may be carried out by a general purposecomputer, as described below.

For purposes of this discussion, any reference to the term “module” orthe term “unit” shall be understood to include at least one of software,firmware, or hardware (such as one or more of a circuit, microchip, anddevice, or any combination thereof), and any combination thereof. Inaddition, it will be understood that each module or unit may includeone, or more than one, component within an actual device, and eachcomponent that forms a part of the described module may function eithercooperatively or independently of any other component forming a part ofthe module. Conversely, multiple modules or units described herein mayrepresent a single component within an actual device. Further,components within a module or unit may be in a single device ordistributed among multiple devices in a wired or wireless manner.

The following Detailed Description of the exemplary embodiments will sofully reveal the general nature of the invention that others can, byapplying knowledge of those skilled in relevant art(s), readily modifyand/or adapt for various applications such exemplary embodiments,without undue experimentation, without departing from the spirit andscope of the disclosure. Therefore, such adaptations and modificationsare intended to be within the meaning and plurality of equivalents ofthe exemplary embodiments based upon the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by those skilled in relevant art(s) in light of theteachings herein.

FIGS. 1A-1C illustrate example diagrams of a human torso showingultrasonic transducer device placement, according to embodiments of thepresent disclosure. In particular, FIG. 1A shows a right side view of atorso 101 of a human onto which both an ultrasonic transducer devicefront probe 102 and a different rear probe 104 are attached to a frontside 103 and dorsal side 105 of the human, respectively. FIG. 1B shows atentative location of the rear probe 104, and FIG. 1C shows a tentativelocation of the front probe 102. In some embodiments, the front and rearprobes may be referred to as first and second probes, respectively.

Although the probes 102, 104 are seen located close to the rightmid-clavicular line 106, it will be appreciated that that these probesmay be located laterally of the line 106 and/or at a different positionalong the direction of the line 106 than the positions shown in FIGS. 1Band 1C. The right mid-clavicular line is denoted as 106, and the leftmid-clavicular line is denoted as 108. If an ultrasound beam is directedtowards the spleen in the body, the probes are preferably locatedadjacent the line 108. If the ultrasound beam is directed towards akidney, the probes are preferably located adjacent either line 106 orline 108, dependent on the selected one of the kidneys in the body.

It will be readily appreciated that measurement of motion of internaltissue region or internal structures is not limited to the liver. Anyparenchymatous soft tissue that can be accessed by ultrasound from thebody surface may be used. In addition to the liver, the spleen and thekidneys may be of particular interest for recording of diaphragm motion,according to some embodiments.

The present invention is described with reference to a currentlypreferred mode of detection involving detecting motion of the liver.This description is used for ease of explaining the structure,principles, and operation of the various embodiments of the inventionand is intended to be exemplary rather than limiting.

FIGS. 2A and 2B illustrate example diagrams of probe locations on thehuman body for motion detection of the liver, spleen, or kidney,according to embodiments of the present disclosure. Similarly to FIG. 1,FIG. 2A illustrates probe locations on the human body 101, in which theprobes 102, 104 are suitably linked or coupled to a processor (e.g.,signal processor 134 shown in FIG. 22) and display 109. FIG. 2Billustrates front probe 102 locations for motion detection of the liver,spleen, or kidney in a patient's body.

FIG. 3 illustrates a rear perspective view of a front ultrasonictransducer device probe 102, according to embodiments of the presentdisclosure. FIG. 4 illustrates a rear plan view of the probe 102 of FIG.3, according to embodiments of the present disclosure.

The ultrasonic transducer device front probe 102 is further describedwith reference to FIGS. 5, 6, 9, and 10. The illustrated probe 102 isconfigured to be placed on a front body surface 103 of a human in orderto direct an ultrasonic beam towards an internal structure and receiveultrasonic echo signals from the internal structure. The internalstructure is at least one of the liver, the spleen, or a kidney of thehuman. In some embodiments, a tissue region may be referred to as aninternal structure inside a patient's body.

The probe illustrated in FIGS. 5, 6, 9 and 10 has a housing 110,suitably made from a hard shell plastic material in a non-limitingexample, with a cavity 111 in which an ultrasonic transducer 112 islocated. A transceiving face 113 of the transducer 112 is oriented at anacute angle Ω relative to a front plane 114 of the housing at oradjacent a cavity mouth of the cavity of the housing. In someembodiments, the acute angle is suitably in a range of 0 to 60 degrees.

The transducer 112 is fixedly located in the cavity 111 of the housing110 by means of at least a body 115 of first material comprising anultrasound non-sonolucent material which extends towards the front plane114. It will be observable that the body 115 of the first materialsurrounds a recess 116 extending from the transceiving face 113 towardsthe front plane 114.

A first part of a body 117 of a second material comprising an ultrasoundsonolucent material is located in the recess 116 at and in front of thetransceiving face 113 of the transducer towards the front plane 114. Asecond part of the body 117 of the second material is in additionapplied onto a front surface 115′ of the body of the first material andmade integrally engaged therewith. In some embodiments, the first andsecond parts of the body 117 are integral.

FIGS. 7, 8, 11 and 12 illustrate additional embodiments of the frontultrasonic transducer device probe. In particular, there is no shellhousing 110 and housing cavity 111 present in the embodiments of FIGS.7, 8, 11 and 12, which differ from the embodiments of FIGS. 5, 6, 9 and10. Instead, in the embodiments of FIGS. 7, 8, 11 and 12, the housing issimply constituted or formed by a body 118 of a first material, suitablyof the same type of material as that of the body 115.

As shown in the embodiments of FIGS. 9-12, it is noted that thetransducer 112 is supported in a different way than that in theembodiments of FIGS. 5-8. For example, in FIGS. 5-8, the transducer 112is supported by a printed circuit board 119 and the body 115. In FIGS.9-12, the recess is lined with an open-ended socket-like member 120 ofultrasound non-sonolucent material, and the transducer 112 is mounted ata bottom region of the open-ended socket-like member 120. The materialof the member 120 exhibits an acoustic dampening property, and an outerwall of the member 120 is configured to engage the body 115, 118 of thefirst material. In FIGS. 9-12, transducer 112 and the open-endedsocket-like member 120 extend from a printed circuit board 119. Themember 120 with the transducer 112 located therein, as well as theprinted circuit board, are supported by and embedded in the body 115,118 of the first material.

The probe 102 also contains an accelerometer unit 121 (shownschematically) and a magnetic field detection unit 122 which areembedded (e.g., encapsulated) in the body 115, 118 of the firstmaterial. The accelerometer unit 121, the magnetic field detection unit122, and the transducer 112 are connected or coupled to the printedcircuit board 119 and to a signal processor 134 (as shown in FIG. 22).The signal processor is further described below with respect to FIG. 22.

The housing 110 having the cavity 111 and the body 115 of first materialare suitably composed of materials having compatible properties, inparticular to bond well together, but suitably also to have e.g. similarthermal expansion properties. For example, materials for the housing 110may include a suitable plastics material or polymer(s) and/or body 115of the first material may include an ultrasound non-sonolucent siliconerubber material or the like. In order to make a silicone rubber materialultrasound non-sonolucent, a variety of possible additives are available(e.g., calcium carbonate, titanium dioxide, zinc oxide, quartz, glass,or other additives). An example of silicone rubber with an additive isELASTOSIL® RT 602 A/B. In order to make a plastics material ultrasoundnon-sonolucent, same or similar additives may be used. Thus, if thesocket-like member 120 is formed of plastics material, such additivesmay be used. In some cases, the acoustic dampening property of suchadditives in silicone rubber or plastics material may be dependent onparticle size and particle mass density (e.g., preferably particledensity being highly different from the density of silicone rubber ofplastic, both being about 1,000 kg/m³).

According to the embodiments of FIGS. 5-8 (e.g., where no housing shell110 is present), the body 118 of first material forming the probehousing has a rear surface region, (e.g., the surface region which doesnot face the skin of the human body), such as that visible in FIGS. 3and 4. In some embodiments, the first material being present thereatpreferably has a non-sticky surface property.

It is noted that in the embodiments of FIGS. 7 and 8, the body 118 of afirst material creates the recess 116, and in FIGS. 11 and 12, the body118 surrounds the socket member 120 in which the transducer is located.The front surface 115′, 118′ of the body 115, 118 of the first materialhas the body 117 of the second material attached thereto. The frontsurface 117′ of the body of the second material may exhibit one of: aninherent tacky property, an attachment face for an adhesive member or adouble-sided tacky tape, and an engagement face for a tacky layer of abody of a third material.

If the front face 117′ of the body 117 of the second material has atacky surface property, the probe may be provided with a removableprotective cover 123, the cover being removable prior to application ofthe probe onto the skin of the body 101. In this particular case, theprobe is of a self-adhesive type suitably for single-use, althoughdouble sided tacky tape may be attached to the face 117′ after a firstuse of the probe, provided that the face 117′ is not contaminated insuch a way that the tape will not adhere.

If the front face 117′ is not to be used for adhering the probe 102directly to the skin, then, as indicated by a general element 124, anadhesive member or the double-sided tacky tape is attached to the frontface 117′ of the body 117 of the second material. The adhesive member ordouble-sided tacky tape may be ultrasound sonolucent at least at aregion faced by the transducer transceiving face 113. Additionally oralternatively, the general element 124 covering the front face 117′ ofthe body 117 of the second material is the tacky layer of a body of athird material being ultrasound sonolucent.

The first and second materials are provided in the probe 102 as anintegral structure, and both materials exhibit similar or compatiblethermal and mechanical properties. Further, the second material and thethird material are at least one of: identical, property compatible, andengagement compatible. The body material type of at least one of thefirst, second and third materials comprises a silicone rubber material.If the first and second materials are similar, the ultrasoundnon-sonolucent first material may have an added component thereto toeffectively obtain its desired properties. For example, an additive,such as calcium carbonate, titanium dioxide, zinc oxide, quartz, glass,or the like, may be added to a silicone rubber material to make thesilicone rubber material non-sonolucent. In an example embodiment, thefirst material is silicone rubber with one or more additives, whereasthe second and third materials are silicone rubber. Many suitablesilicone rubber materials are commercially available. For example, anultrasound non-sonolucent silicone rubber material is ELASTOSIL® RT 602A/B, and an ultrasound sonolucent material is ELASTOSIL® RT 601 A/B. Inpractice, it is important that additives do not interfere with thesetting procedure of the silicone rubber and are biocompatible andexhibit excellent adherence to the silicone rubber material.

FIG. 13 illustrates a perspective, front full view of the probe of FIGS.9 and 10, prior to installation of first and second materialsencapsulated in the probe, according to embodiments of the presentdisclosure. In particular, FIG. 13 shows the probe 102 prior toinstallation of an embedding (e.g., encapsulating) body 115 of a firstmaterial and application of a body 117 of a second material to fill therecess 116 down to the transducer transceiving face 113 and further tocover a front face 115′ to the body 115 of the first material.

FIG. 14 illustrates another perspective, front full view of the probe102 as shown in FIG. 13, from a different angle, whereas FIG. 15illustrates a perspective, front sectioned view of the probe 102 asshown in FIGS. 13 and 14, according to embodiments of the presentdisclosure. Wiring from a cable 125 onto the printed circuit board 119has not been shown for sake of clarity. In some embodiments, cable 125provides electrical connections between circuit board 119, processor,and display 109 (see FIG. 2A).

As discussed above, the first, front probe 102 is configured tocooperate or interface with a second, rear probe 104. These probes(shown in FIGS. 1A, 1B, 1C, 2A, and 2B) are included in a respirationdetection system configured to be located on a body surface of a human.

In the front probe 102, the ultrasonic transducer 112 is stationarylocated as described in reference to FIGS. 5-12 to produce an ultrasoundbeam directed outward from front surface plane 114 and towards aninternal structure or a tissue region inside the body. Further, theprobe 102 incorporates the first accelerometer unit 121 and the firstmagnetic field unit 122.

The second, rear probe 104 is shown in further detail in FIGS. 16-21.The probe 104 has a housing 126 in the form of a shell member of aplastics material and with an associated cavity 127 in which a secondaccelerometer unit 128 and a second magnetic field unit 129 arestationary located and suitably connected to a common printed circuitboard 130. Wires from a cable 131 connecting to the printed circuitboard are not shown for sake of clarity. In some embodiments, cable 131provides electrical connections between circuit board 130, processor,and display 109 (see FIG. 2A).

The transducer 112, the first and second accelerometer units 121, 128,and the first and second magnetic field units 122, 129 are linked to thesignal processor 134, as will be further described with reference toFIG. 22. The second accelerometer unit 128 provides for measurement oftilt angles of a surface supporting the dorsal side of the human body.The magnetic field sensor device of the first magnetic field unit 122 isa magnetic pickup coil in the illustrated embodiment. In an embodiment,the first and second accelerometer units 121, 128 exhibit at least twoaccelerometers each. In an embodiment, the first accelerometer unit 121includes a three-axis accelerometer device.

Output signals provided to the signal processor 134 from the first andsecond accelerometer units 121, 128 and by use of the first and secondmagnetic field units 122, 129 are a function of spatial positionalmovements and orientation of the first probe 102 attached to the frontside of the patient during respiration. The spatial positional movementand orientation is related to at least one of heave, roll, pitch and yawtype movements resulting from breathing by the patient.

The second accelerometer unit 128 and the second magnetic field unit 129are stationary located in the cavity 127 of second housing 126 by meansof a body 132 of a fourth material.

A front face plane 132′ of the body 132 of the fourth material providesone of: a tacky property, an attachment face for an adhesive member or adouble-sided tacky tape, and an engagement face for a tacky layer of abody of a fifth material. In FIG. 21, at least one of the adhesivemember, a double-sided tacky tape, and an engagement face for a tackylayer of a body of a fifth material is generally denoted by referencenumeral 133.

At least one of the first, second, third, fourth, and fifth materials issuitably of a silicone rubber type. In order to avoid possible skinsores on the dorsal side of the body, at least a surface area of thesecond probe to abut or contact a dorsal skin area of the human bodyexhibits a biocompatible material, the abutting surface area of thesecond probe (e.g., the area of the probe surface in contact with skin)suitably being in the range of 5-100 cm². In the example embodimentdescribed above, the first material is silicone rubber with an additiveincluded to make the silicone rubber ultrasound non-sonolucent, and thesecond and third materials are ultrasound sonolucent silicone rubber.Continuing with the example embodiment, the fourth and fifth materialsare silicone rubber. In some embodiments, the fourth and fifth materialsmight not need to take into consideration ultrasound aspects, because anultrasound transducer might not be present in the dorsally locatedsecond probe 104. In additional embodiments, the first, second, third,fourth, and fifth materials are commercially available.

In some embodiments, the signal processor 134 (shown in FIG. 22)controls intensity, frequency and duration of magnetic field to begenerated by the second magnetic field unit. The signal processor isconfigured to calculate, based on inputs from the first and secondaccelerometer units 121 and 128 and from the first magnetic field unit122 interacting with the second magnetic field unit 129, movement andorientation of the abdominal wall of the patient's body in relation todirection of expected motion of the internal structure in question. Themovement and orientation being related to respiration parametersassociated with the abdominal muscles of the patient.

As described above, the internal structure or tissue region of thepatient is at least one of the liver, spleen, or kidney of the patient.It will be readily appreciated that detected motion of the internalstructure is a function of thoracic diaphragm movement in the patient'sbody.

As shown in FIG. 22, the processor 134 has associated therewith a datastorage 135, to store respiration data of a patient during the course ofmonitoring, and a display 136 to observe visual representation ofcurrent or stored respiration data. The processor 134 also includestherein a transceiver section 134′ operating with the transducer 112. Insome embodiments, the processor 134 may cause a respiration alert unit137 to generate one or more visual and/or audible alerts if one or morerespiration parameters of the patient moves away from acceptableparameter ranges. Suitably, the front probe 102 has a first probeidentity serial number device 138, and similarly the rear probe 104 hasa second probe identity serial number device 139. These serial numbers138, 139 are unique to the respective probes in use and might not beable to be changed.

Further, a registration and operation comparator unit 140 is providedand linked or coupled to the processor 134. In some embodiments, apatient's identity serial number (e.g., a social security, a taxpersonal code, or another identifier) may be entered into the unit 140using a keyboard 141 which is linked to the processor 134, prior toand/or during use of the respiration detection system on a patient. Inparticular, with use on an infectious patient, it may be important thatthe front and rear probes 102, 104 when removed are not used on anotherpatient. The unit 140 may therefore include an operation mode controllerthat prevents such second-hand use. In other cases, second-hand use maybe acceptable if the probes 102, 104 are re-used on the originalpatient, and not on a new patient.

In some embodiments, reliability of a probe may deteriorate over time ifthe probes 102, 104 are re-used too many times. Thus, the operation modecontroller may electronically limit numbers of re-use of a probe to apredefined number of uses, e.g., 3 to 10 uses, whereafter the processor134 and the unit 140 may effectively block the serial numbers from thedevices 138, 139. In other cases, the probes 102, 104 may have arespective self-tacky front face 117′, 132′, as typically could be usedby an ICU (Intensive Care Unit) for single use. For these single-useprobes, the probe identities may be blocked once the system is shutdown, and the probes are removed from the patient. In some embodiments,a power supply 142 may deliver power to the processor 134, the datastorage 135, the display 136, and the units 137, 140. In additionalembodiments, required power to the probes 102, 104 are delivered via theprocessor 134.

An example method for motion compensation of measurement errors duringrespiration monitoring is described herein with reference to FIGS.23-26. In order to more easily appreciate the functions of the systems,reference is also made to FIG. 27, which schematically illustratesderivation of signals from accelerometers in the front and rear probes,and FIG. 28, which schematically illustrates signal processing relatedto range calculation and motion compensation, according to embodimentsof the present disclosure.

The example method is used in ultrasound-based detection of respirationparameters of a patient. The detection uses an ultrasound beam 143directed from and to an ultrasound transducer device 112 in a frontprobe 102 (located on a front side of the human body). The ultrasoundbeam 143 is directed from a front body surface of the human to aninternal structure or a tissue region inside the body and is reflectedback to the probe 102 as ultrasound echo signals.

In an embodiment, the method comprises:

(a) attaching a first probe 102 to a front body surface of the patient,the first probe 102 having the ultrasound transducer 112, the firstaccelerometer unit 121, and the first magnetic field unit 122,

(b) attaching a second probe 104 to a dorsal body surface of thepatient, the second probe 104 having the second accelerometer unit 128,and the second magnetic field unit 129,

(c) providing the signal processor 134 coupled to the transducer 112,the first and second accelerometer units 121, 128, and the first andsecond magnetic field units 122, 129,

(d) transmitting, from the ultrasound transducer 112 in the first probe102, an ultrasound beam into an internal structure (or tissue region)inside the body of the patient,

(e) receiving, at the ultrasonic transducer 112 in the first probe 102,ultrasound echo signals from the internal structure,

(f) generating, by the second magnetic field unit 129, a magnetic fieldtransmitted to and detected by the first magnetic field unit 122,

(g) calculating, using the signal processor 134, the orientation of thefirst accelerometer unit 121 relative to a fixed coordinate frame usingderived parameters from the unit 121, and further calculating derivedparameters as unit vectors representing an orientation of the ultrasoundbeam 143 (see FIGS. 23-26) and an orientation of the first magneticfield unit,

(h) calculating, using the signal processor 134, the orientation of thesecond accelerometer unit 128 relative to a fixed coordinate frame usingderived parameters from the unit 128, and further calculating derivedparameters including: body back support tilt angle (a) and unit vectorsrepresentative of a spatial direction from the second magnetic fieldunit 129 (e.g., an electromagnet) to the first magnetic field unit 122(e.g., a sensor device located in the front probe 102), an orientationof the second magnetic field unit 129, and an expected direction ofmotion of the internal structure or tissue region (e.g., liver, spleenor kidney) during exhalation,

(i) calculating in the signal processor 134 any varying distance betweenthe first and second magnetic field units 122, 129 based on thedetection of the magnetic field, and

(j) processing, using the signal processor 134, the results fromcalculations in steps (g)-(i) to generate correction parameters tocompensate for measurement errors in received ultrasound echo signalscaused by abdominal wall movement due to respiration of the patient.

More specifically, the processing step (j) may comprise:

(k) decomposing a vector representing the distance between the firstmagnetic field unit 122 contained in the front probe 102 and thedorsally located second magnetic field unit 129 along the ultrasoundbeam direction 143,

(l) differentiating the decomposed vector in time representing thedistance to yield incremental motion values,

(m) adding the incremental motion values in step (l) to incrementalDoppler effect motion values as detected by use of ultrasound echosignals from the internal structure in at least a same time interval,

(n) correcting the added motion values of step (m) for an instantaneouscosine value of an angle between the ultrasound beam 143 and directionof motion of the internal structure, and

(o) summing the corrected and added motion values in order to obtaininternal structure position variations describing corrected respiratoryparameters.

The need for motion correction of the front probe will now be discussedin further detail below. Although the following discussion is primarilyrelated to aspects of liver motion detection, it will be appreciatedthat embodiments of the disclosure may also be applied to motiondetection of other tissues, such as the spleen or a kidney of the human.

During a pilot clinical study for evaluation of an ultrasound transducerdevice probe, it was observed that reproducibility of measurementsprovided by such an instrument was poor, and that re-positioning of theprobe on the abdominal surface resulted in undesirable changes ordeviations in the measured liver (and diaphragm) motion amplitudes. Byanalyzing possible causes for this, two factors were identified thatmight have contributed to the deviations.

First, the probe on the abdominal surface of a patient is moving up anddown when the patient is breathing. This motion has a vector componentalong the ultrasound beam direction 143, and the motion of the probegives a variable under-estimation of the true motion of the liver 144,as illustrated in FIGS. 23 and 24. When the liver 144 moves towards theprobe 102 during inhalation, the probe will at the same time move awayfrom the liver, and vice versa during exhalation. This occurrence wasconfirmed experimentally using a mechanically fixed probe that was notallowed to move, resulting in about 40% higher estimates of liver motioncompared to a freely moving probe.

FIGS. 23 and 24 illustrate cross-section diagrams showing basicprinciples for respiration detection using ultrasound beam directed at ahuman liver and motion of a chest and abdominal region of the human bodyduring respiration, according to embodiments of the present disclosure.In particular, the cross-section diagrams of FIGS. 23 and 24 show themotion 145 of the liver 144 and the motion 146 of the probe, and how themotion of the probe can be considered as having two components. Onecomponent 147 is along the ultrasound beam direction 143. This componentwill directly affect and disturb the estimated motion of the liver 144.

Second, the abdominal surface is conical, and not cylindrical. Thisabdominal shape will cause a variable tilt of the transducer 112 and theprobe 102, and will thus affect the direction of the ultrasound beam143. Just below the costal margin where the front probe 102 is placed inorder to have acoustic access to the liver 144, there may be asubstantial concavity of the surface in slim human subjects. And inobese human subjects, the surface is convex, as illustrated in FIG. 25.Thus, assumption of a fixed 45° angulation between the sound beam 143and the direction 145 of the liver motion might not be valid.

Accordingly, embodiments of the present invention alleviate the issuesdiscussed above.

FIG. 26 illustrates a cross-section diagram showing the basic principleof distance measurement 148 through use of placement of a dorsal(ancillary) or rear sensor probe 104. In the non-limiting example, thehuman body is supine on a bed mattress (e.g., lying face upward).

The probe 102 is equipped with a 3-axis accelerometer module that usesthe direction of the gravity vector to estimate tilt, allowingcalculation of the actual spatial direction of the ultrasound beamrelative to the motion of the liver.

In an embodiment, the extra, second (ancillary) sensor rear probe 104 isadded at a location on the patient's dorsal side, vertically below thefront probe 102 if the patient body is supine. If the patient is in anupright posture, the front and rear probes 102, 104 may be aligned,roughly at right angles to the spine direction of the human.

The rear, second sensor probe 104 contains the additional accelerometerunit 128 for measuring the tilt angle of a bed upon which the patientrests, since most ICU patients have an elevated bed. The tilt anglemeasurement may be utilized in order to have an estimate of the actualliver motion direction.

The rear sensor probe 104 also contains an electromagnet in the unit 129that generates a weak alternating magnetic field that is sensed by amagnet pick-up coil in unit 122 of the front probe 102. The use of theelectromagnet and magnet pick-up coil allows for a continuousmeasurement of the up and down motion of the front probe 102 based onknown relations between magnetic field strength and distance. Byobtaining these calculations, the motion of the probe 102 can then beincluded in the estimate of liver motion.

It will thus be appreciated that precise knowledge about probeorientation and vertical motion allows compensation for the effects ofboth front probe motion and abdominal surface shape.

In development of embodiments of the invention, some potential safetyissues were addressed.

Magnetic field: The electromagnet on the patient's back generates a weakmagnetic field, suitably at a frequency of 33 kHz, that decays with theinverse cube of the distance. In all directions, the field strength isbelow 27 μT at distances of more than 15 mm from the cylindrical magnetcenterline. For example, 27 μT is the recommended maximum magnetic fieldstrength for continuous whole-body exposure to the public at frequenciesbetween 3 kHz and 10 MHz. This means that a few milliliters of skin andsubcutaneous tissues close to the back sensor will be exposed to fieldstrengths above 27 μT, but always below 100 μT which is thecorresponding limit for continuous occupational whole-body exposure.

New Acceleration and Magnetic Sensor Devices in the Front Probe 102 andthe Acceleration Sensor Device 128 in the Rear Probe:

The accelerometers 121, 128 and the magnetic pickup coil 122 that havebeen added to the probes 102, 104 are passive devices without any energyemissions. They therefore do not have any potential for harming thepatient.

Physical Pressure Sores on the Dorsal Side of the Patient:

The rear sensor probe 104 might have a potential for creating pressuresores. This has been considered during the design of the sensor. In oneembodiment, the probe 104 is suitably encapsulated in a biocompatiblesoft silicone rubber, and has, e.g., a circular 5 cm diameter flatcontact surface for contact with a patient's skin or a surface in therange of 5 to 100 cm², without sharp edges and with a tapered shapetowards its circumference. A suitable attachment location is the backflank of a patient which is a soft tissue region between the rib cageand the pelvis, contributing to an even mechanical pressuredistribution. In one embodiment, the attachment to the skin is by usingone of the several attachment options used for the front probe, such asa double-sided silicone rubber tape. If the body of the fourth materialor the fifth material is tacky, the rear probe may be attached to thedorsal side of the human body via one of these tacky materials.

In order to prevent pressure sores, the skin in and around the sensorattachment area may be carefully inspected during daily re-attachmentsof the rear probe, and also during routine nursing visits to thepatient. The occurrence of skin irritation may be recorded as an adverseevent, and the patient in such a situation may be excluded from furtherparticipation.

Electrical safety: Both probes 102, 104 are fully and hermeticallyencapsulated, suitably in electrically insulating material, such assilicone rubber with an electrical insulation of 20 kV/mm. In anembodiment, the shortest distance from an electrical conductor insidethe probe to the surface is at least 1 mm. At least the bodies of thefirst and the fourth materials exhibit such electrical insulationproperties.

In some embodiments, the device is suitably powered from a medical gradeexternal power supply delivering 12 VDC. The highest voltage foundinside the device is preferably not more than 18 to 24 VDC.

Example Embodiment: Motion Compensation

A simplified method of motion compensation based on accelerometerreadings of the gravity vector in combination with magnetic rangemeasurements will now be discussed. It is assumed, for the sake of asimplified presentation, that the sensor probe 102 motion issubstantially along a direction perpendicular to the plane of themattress on which the human body of the patient rests.

Rear (Aux) Sensor Probe 104 Orientation

Calculation of the rear sensor probe orientation (e.g., the probe 104located on the dorsal side of the patient) may be expressed as arotation matrix relative to the global coordinate frame, and calculationof derived parameters:

-   -   Sine and cosine of mattress tilt angle (a); and    -   Unit vectors describing:        -   Direction from rear probe 104 to front probe 102. This is            also the expected motion direction of the front probe 102,        -   The orientation of the electromagnet 129, and        -   Direction of expected liver motion 145, a positive direction            being towards the patient's head.            Front Sensor Probe Orientation

Calculation of the front probe 102 orientation, with derived parameters,are based on the inputs of the accelerometer 121 readings and tilt ofthe mattress from the rear (aux) probe 104.

Based on the user instructions about how to orient the front probe andthe rear probe, outputs are:

-   -   Unit vectors describing:        -   Ultrasound beam direction 143        -   Magnet pick-up orientation 149            Distance from Rear Probe to Front Probe

The distance is calculated from the magnetic pick-up signal, thedirection from the electromagnet 129 to the pick-up 122, and theorientations of the electromagnet 129 and the pick-up signal 122. Thiscalculation also utilizes a single calibration value (k) determinedduring production of the system.

Motion Compensation

The distance 148 between the rear probe and the front probe isdecomposed along the sound beam direction 143 and differentiated to giveincremental motion. This is added to the incremental motion detected bythe Doppler system in the same time interval. The summed motion is thencorrected for the instantaneous cosine of the angle between the soundbeam and the liver motion direction. Displacement is then calculated byintegration.

General Aspects

All accelerometer readings are converted to conform with a coordinatesystem where the axis directions are:

X: Towards patient's head,

Y: Towards patient's left arm side, and

Z: Downwards.

Assuming that the IMUs (inertial measurement units) of the three-axisaccelerometers are mounted at integer multiples of 90°, coordinatesystem conversion be done by a combination of permutations and signreversals.

All coordinates and rotations in formulas and illustrations are given inthe global stationary coordinate system unless otherwise specified.

For the calculations below, where the accelerometer readings only areused for determination of angular orientations, they do not need to beconverted from raw binary format to metric units, as long as the numericformat is signed.

Rear Probe 104 Orientation:

Accelerometer readings are: a_(Ax), a_(Ay), and a_(Ax) (signed,arbitrary units)

It is assumed that the electrical cord points straight outwards to thepatients' right side, and that the cord, ferrite rod and accelerometery-axis are parallel.

The orientation of the probe 104 may be described by a sequence of tworotations:

-   -   1) An initial rotation of ρ around the global x-axis to account        for the local transverse curvature of the patients back (roll);        and    -   2) A rotation of a around the global Y-axis to account for the        tilt of the bed (pitch).

The rotations are derived by considering the probe and its measuredgravity vector as a stiff body, and performing rotations that aligns thegravity vector with the negative global z-axis. The first rotationaligns the gravity vector with the x-z plane. For example, FIG. 29illustrates an example graph showing a first rotation (p) seen from thepositive x-axis, which can be calculated as follows:

$\begin{matrix}{{\sin(\rho)} = {\frac{- a_{Ay}}{\sqrt{a_{Ay}^{2} + a_{Az}^{2}}}\mspace{14mu}{and}}} & {{Eqn}.\mspace{14mu}(1)} \\{{\cos(\rho)} = \frac{- a_{Az}}{\sqrt{a_{Ay}^{2} + a_{Az}^{2}}}} & {{Eqn}.\mspace{14mu}(2)}\end{matrix}$

And the corresponding rotation matrix is:

$\begin{matrix}{R_{A\; 1} = \begin{bmatrix}1 & 0 & 0 \\0 & {\cos(\rho)} & {- {\sin(\rho)}} \\0 & {\sin(\rho)} & {\cos(\rho)}\end{bmatrix}} & {{Eqn}.\mspace{14mu}(3)}\end{matrix}$

FIG. 30 shows an example of orientation of the gravity vector prior tothe second rotation as seen from the positive y-axis. The secondrotation is calculated as follows:

$\begin{matrix}{g_{A} = \sqrt{a_{Ax}^{2} + a_{Ay}^{2} + a_{Az}^{2}}} & {{Eqn}.\mspace{14mu}(4)} \\{{\sin(\alpha)} = {\frac{a_{Ax}}{g_{A}}\mspace{14mu}{and}}} & {{Eqn}.\mspace{14mu}(5)} \\{{\cos(\alpha)} = \frac{\sqrt{a_{Ay}^{2} + a_{Az}^{2}}}{g_{A}}} & {{Eqn}.\mspace{14mu}(6)}\end{matrix}$

Note that sin(α) and cos(α) are normally utilized for calculation offront probe 102 orientation. The angle α itself might not need to beevaluated.

The corresponding rotation matrix is:

$\begin{matrix}{R_{A\; 2} = \begin{bmatrix}{\cos(\alpha)} & 0 & {\sin(\alpha)} \\0 & 1 & 0 \\{- {\sin(\alpha)}} & 0 & {\cos(\alpha)}\end{bmatrix}} & {{Eqn}.\mspace{14mu}(7)}\end{matrix}$

The full rotation is thus:R _(aux) =R _(A2) R _(A1)  Eqn. (8)

The unit vector orientation of the electromagnet in the second magneticfield unit 129 of the rear probe 104 is:

$\begin{matrix}{{\hat{v}}_{magnet} = {R_{aux}\begin{bmatrix}0 \\1 \\0\end{bmatrix}}} & {{Eqn}.\mspace{14mu}(9)}\end{matrix}$

The unit vector direction of liver motion expressed in the globalcoordinate system is:

$\begin{matrix}{{\hat{v}}_{liver} = {{R_{A\; 2}\begin{bmatrix}1 \\0 \\0\end{bmatrix}} = \begin{bmatrix}{\cos(\alpha)} \\0 \\{- {\sin(\alpha)}}\end{bmatrix}}} & {{Eqn}.\mspace{14mu}(10)}\end{matrix}$

The unit vector from the rear electromagnet 129 to the front sensorpickup 122 is:

$\begin{matrix}{{\hat{v}}_{m\; m} = {{R_{A\; 2}\begin{bmatrix}0 \\0 \\{- 1}\end{bmatrix}} = \begin{bmatrix}{- {\sin(\alpha)}} \\0 \\{- {\cos(\alpha)}}\end{bmatrix}}} & {{Eqn}.\mspace{14mu}(11)}\end{matrix}$Front Probe 102 Orientation:

Accelerometer readings are: a_(Px), a_(Py), and a_(Pz)

Bed tilt angle is: α (from back sensor, expressed as sin(α) and cos(α)).

A sequence of rotations that positions the probe 102 in a manner thatmakes the measured acceleration vertical and upwards, and assures thatthe probe 102 x-axis and the body centerline are in the same plane are:

-   -   1) A rotation of φ around y to account for the local taper of        the body surface;    -   2) A rotation of θ around x to account for the position of the        probe 102 in the right flank; and    -   3) A final rotation of a (bed tilt) around y.

The calculations are derived by finding the sequence of rotations of astiff body consisting of the probe 102 and its associated measuredgravity vector that aligns the measured gravity vector with the globalnegative z-axis (upwards).

For rotation (1), the initial condition is presented by Equations 12-19below and illustrated by FIG. 31. For example, FIG. 31 illustrates probecoordinates and measured acceleration seen from the positive y-axis. Thefirst rotation is around the y-axis with an angle of φ=β−γ which causesthe measured acceleration vector to point such that a remaining distanceto the global y-z plane is g_(P) sin(α).

The equations include:

$\begin{matrix}{g_{P} = \sqrt{a_{Px}^{2} + a_{Py}^{2} + a_{Pz}^{2}}} & {{Eqn}.\mspace{14mu}(12)} \\{{\sin(\beta)} = {\frac{a_{Px}}{\sqrt{a_{Px}^{2} + a_{Pz}^{2}}}\mspace{14mu}{and}}} & {{Eqn}.\mspace{14mu}(13)} \\{{\cos(\beta)} = \frac{- a_{Pz}}{\sqrt{a_{Px}^{2} + a_{Pz}^{2}}}} & {{Eqn}.\mspace{14mu}(14)} \\{{\sin(\gamma)} = {\frac{g_{P}{\sin(\alpha)}}{\sqrt{a_{Px}^{2} + a_{Pz}^{2}}}\mspace{14mu}{and}}} & {{Eqn}.\mspace{14mu}(15)} \\{{\cos(\gamma)} = \sqrt{1 - {\sin^{2}(\gamma)}}} & {{Eqn}.\mspace{14mu}(16)}\end{matrix}$

It should be noted that the following condition is to be fulfilled forvalid calculations:

${{g\mspace{11mu}{\sin(\alpha)}}} \leq \sqrt{a_{Px}^{2} + a_{Pz}^{2}}$

In some embodiments, user errors in probe 102 placement (e.g., improperorientation) might cause this condition. If this happens, an errormessage may be given, and the session may be re-started.

The rotation angle φ has the following properties:cos(ϕ)=cos(β−γ)=cos(β)cos(γ)+sin(β)sin(γ)  Eqn. (17)sin(ϕ)=sin(β−γ)=sin(β)cos(γ)−cos(β)sin(γ)  Eqn. (18)

The rotation matrix is thus:

$\begin{matrix}{R_{P\; 1} = \begin{bmatrix}{\cos(\phi)} & 0 & {\sin(\phi)} \\0 & 1 & 0 \\{{- \sin}\;(\phi)} & 0 & {\cos\;(\phi)}\end{bmatrix}} & {{Eqn}.\mspace{14mu}(19)}\end{matrix}$

For rotation (2), the situation is illustrated by FIG. 32 and relatedEquations 20-22. For example, FIG. 32 shows the situation after rotation(1) seen from the global positive x-axis. The next rotation (2) aroundthe global x-axis may bring the acceleration vector into the global x-zplane. The equations include:

$\begin{matrix}{{\sin(\theta)} = {\frac{- a_{Py}}{g_{P}{\cos(\alpha)}}{and}}} & {{Eqn}.\mspace{14mu}(20)} \\{{\cos(\theta)} = \sqrt{1 - {\sin^{2}(\theta)}}} & {{Eqn}.\mspace{14mu}(21)}\end{matrix}$

The rotation matrix is thus:

$\begin{matrix}{R_{P\; 2} = \begin{bmatrix}1 & 0 & 0 \\0 & {\cos(\theta)} & {- {\sin(\theta)}} \\0 & {\sin(\theta)} & {\cos(\theta)}\end{bmatrix}} & {{Eqn}.\mspace{14mu}(22)}\end{matrix}$

FIG. 33 shows the direction of the measured acceleration vector afterrotation (2). The last rotation around the global y-axis will align thevector with the negative z-axis of the global coordinate system.

For rotation (3), the rotation matrix:

$\begin{matrix}{R_{P\; 3} = \begin{bmatrix}{\cos(\alpha)} & 0 & {\sin(\alpha)} \\0 & 1 & 0 \\{- {\sin(\alpha)}} & 0 & {\cos(\alpha)}\end{bmatrix}} & {{Eqn}.\mspace{14mu}(23)}\end{matrix}$

As a note, R_(P3) may be the same as R_(A2), from Eqn. (7) and might notneed to be recalculated.

The full rotation is then calculated as follows:R _(front) =R _(P3) R _(P2) R _(P1)  Eqn. (24)

The ultrasound beam direction (45° downwards) is:

$\begin{matrix}{{\hat{v}}_{beam} = {R_{front}\begin{bmatrix}{\cos\left( {45{^\circ}} \right)} \\0 \\{\sin\left( {45{^\circ}} \right)}\end{bmatrix}}} & {{Eqn}.\mspace{14mu}(25)}\end{matrix}$

In some embodiments, these trigonometric functions are preferablypre-calculated.

The orientation of the magnet pickup 122 (angled, in one embodiment, at26° rotation around the probe x-axis) is:

$\begin{matrix}{{\hat{v}}_{pickup} = {R_{front}\begin{bmatrix}0 \\{\cos\left( {26{^\circ}} \right)} \\{\sin\left( {26{^\circ}} \right)}\end{bmatrix}}} & {{Eqn}.\mspace{14mu}(26)}\end{matrix}$

In some embodiments, these trigonometric functions are also preferablypre-calculated.

Magnet Distance Measurements 148:

The inputs to the calculation of distance are:

N_(cal): The signal reading during calibration. It is assumed that theemitting magnets in the second magnetic field unit 129 and the receivingmagnets in the first magnetic field unit 122 are oriented parallel witheach other on a flat surface and orthogonal to the distance betweentheir centerlines when the system is calibrated;

S_(cal): The distance between the magnets 122, 129 during calibration;

N_(meas): The signal reading during measurements;

v_(mm): Unit vector from magnet 129 to pickup 122;

v_(magnet): Unit vector giving the orientation of the electromagnet 129;and

v_(pickup): Unit vector giving the orientation of the magnet pickup 122in the front probe 102.

The formula for the external magnetic field from a dipole is calculatedas follows:

$\begin{matrix}{B = {\frac{\mu }{S^{3}}\left\lbrack {{3{\left( {{\hat{v}}_{magnet} \cdot {\hat{v}}_{m\; m}} \right) \cdot {\hat{v}}_{m\; m}}} - {\hat{v}}_{magnet}} \right\rbrack}} & {{Eqn}.\mspace{14mu}(27)}\end{matrix}$

S is the distance from the dipole along the direction given by v_(mm),and |μ| is the magnitude of the magnet dipole moment. Note thatmultiplications of vectors with vectors are scalar products. Acircumflex ({circumflex over ( )}) indicates a unit vector.

The received signal (N_(meas)) from the pickup coil 122 will be thecomponent of the field that is parallel with the pickup 122 according tothe following equation:

$\begin{matrix}{N_{meas} = {{\frac{k}{S^{3}}\left\lbrack {{3{\left( {{\hat{v}}_{magnet} \cdot {\hat{v}}_{m\; m}} \right) \cdot {\hat{v}}_{m\; m}}} - {\hat{v}}_{magnet}} \right\rbrack} \cdot {\hat{v}}_{pickup}}} & {{Eqn}.\mspace{14mu}(28)}\end{matrix}$

Here, k is a constant that combines |μ|, the physical properties of thecoils, amplification, ADC properties, demodulation and signal averaging.The constant k is determined by a calibration procedure.

Solving Equation 28 with respect to S gives the following distance(S_(mag)):

$\begin{matrix}{S_{mag} = \sqrt[3]{{\frac{k}{N_{meas}}\left\lbrack {{3{\left( {{\hat{v}}_{magnet} \cdot {\hat{v}}_{m\; m}} \right) \cdot {\hat{v}}_{m\; m}}} - {\hat{v}}_{magnet}} \right\rbrack} \cdot {\hat{v}}_{pickup}}} & {{Eqn}.\mspace{14mu}(29)}\end{matrix}$Calibration:

K is determined during calibration. Assuming that the ferrite rods arelocated at a distance of S_(cal) from each other, and oriented asindicated by FIG. 34, then solving Equation 28 provides:

$\begin{matrix}{k = \frac{N_{cal}S_{cal}^{3}}{\left\lbrack {{3{\left( {{\hat{v}}_{magnet} \cdot {\hat{v}}_{m\; m}} \right) \cdot {\hat{v}}_{m\; m}}} - {\hat{v}}_{magnet}} \right\rbrack \cdot {\hat{v}}_{pickup}}} & {{Eqn}.\mspace{14mu}(30)}\end{matrix}$

Inserting values for vectors v_(magnet), v_(pickup) and v_(mm) thatdescribes the geometry of the calibration setup in FIG. 34 results in:

$\begin{matrix}{k = {\frac{N_{cal}S_{cal}^{3}}{\left\lbrack {{3{\left( {\begin{bmatrix}0 \\1 \\0\end{bmatrix} \cdot \begin{bmatrix}1 \\0 \\0\end{bmatrix}} \right) \cdot \begin{bmatrix}1 \\0 \\0\end{bmatrix}}} - \begin{bmatrix}0 \\1 \\0\end{bmatrix}} \right\rbrack \cdot \begin{bmatrix}0 \\1 \\0\end{bmatrix}} = {{- N_{cal}}S_{cal}^{3}}}} & {{Eqn}.\mspace{14mu}(31)}\end{matrix}$

Note that the measurement units for S_(cal) are the same as the unitsfor S_(mag). If calibration is performed with the pickup rotated 26°(placing the assembled probe on a flat surface), then k instead becomes:

$\begin{matrix}{k = {\frac{N_{cal}S_{cal}^{3}}{\left\lbrack {{3{\left( {\begin{bmatrix}0 \\1 \\0\end{bmatrix} \cdot \begin{bmatrix}1 \\0 \\0\end{bmatrix}} \right) \cdot \begin{bmatrix}1 \\0 \\0\end{bmatrix}}} - \begin{bmatrix}0 \\1 \\0\end{bmatrix}} \right\rbrack \cdot \begin{bmatrix}0 \\{\cos\left( {26{^\circ}} \right)} \\{\sin\left( {26{^\circ}} \right)}\end{bmatrix}} = {- \frac{N_{cal}S_{cal}^{3}}{\cos\left( {26{^\circ}} \right)}}}} & {{Eqn}.\mspace{14mu}(32)}\end{matrix}$Practical Implementation of Calibrated Distance Measurements:

The constant k is determined during production of each system of probesaccording to Equation 31 and is stored in non-volatile memory. In thisexample embodiment described herein, a practical value for S_(cal) is0.25 m.

Motion Compensation

The motion compensation method described herein compensates forcontinuous variations in beam orientation, bed angle, and abdominalsurface motion. It assumes that the abdominal surface moves in adirection (v_(mm)) perpendicular to the mattress.

Data from the different sensors in the probes are pre-conditioned tohave identical sample rates and delays, and the sign of theultrasound-based range measurements (S_(ultr)) is such that motion ofthe liver towards the patients head is positive. The letter delta (Δ)signifies differences between consecutive samples.

The incremental motion of the liver between two successive sample pointswhen corrected for the angle between the magnet range measurement andthe ultrasound beam, and for angle between the ultrasound beam and livermotion is:

$\begin{matrix}{{\Delta\; S_{liver}} = \frac{{\Delta\;{S_{mag}\left( {{\hat{v}}_{m\; m} \cdot {\hat{v}}_{beam}} \right)}} + {\Delta\; S_{ultr}}}{{\hat{v}}_{beam} \cdot {\hat{v}}_{liver}}} & {{Eqn}.\mspace{14mu}(33)}\end{matrix}$

It may be noted that if v_(beam) and v_(liver) are close toperpendicular to each other, (e.g. as (|{circumflex over(v)}_(beam)·{circumflex over (v)}_(liver)|<0.2)), an error message orwarning may be issued since measurements then will be veryangle-dependent and inaccurate.

The instantaneous velocity of the liver 144 is found as:

$\begin{matrix}{{{Velocity} = \frac{\Delta\; S_{liver}}{\Delta\; t}};} & {{Eqn}.\mspace{14mu}(34)}\end{matrix}$

-   -   where Δt is the time between samples.

The position of the liver is found by summation of ΔS_(liver).

Thus, it may be summarized that in order to compensate for movementdetection errors related to an internal structure of one of the liver,the spleen, and a kidney of the human, it is useful to exploit a 3-axisaccelerometer unit in the front and rear probes to measure tilt based ondirection of gravity, and using the magnetic field unit in the frontprobe to measure up and down motion of the probe with the assistance ofthe second magnetic field unit which emits a magnetic field. By addingthe rear probe to be located on the dorsal side of the human, that probehaving the second accelerometer unit, it is also possible to measuretilt angle of a bed on which the patient rests, assuming that the livermoves along the same direction as the bed surface. It is then possibleto compute an angle between liver motion and an ultrasound beam insteadof assuming that the beam has a stationary value of, e.g., 45°. Thepresent disclosure thereby offers the possibility to computecontribution of up and down motion to the ultrasound Doppler signalprovided, and thereby compensate for the related signal errors.

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections may set forth one or morebut not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

Embodiments of the present invention have been described above with theaid of functional building blocks illustrating the implementation ofspecified functions and relationships thereof. The boundaries of thesefunctional building blocks have been arbitrarily defined herein for theconvenience of the description. Alternate boundaries can be defined solong as the specified functions and relationships thereof areappropriately performed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

What is claimed is:
 1. A method for motion compensation inultrasound-based detection of respiration parameters of a human, themethod comprising: attaching a first probe to a front body surface ofthe human, the first probe having an ultrasonic transducer, a firstaccelerometer unit, and a first magnetic field unit; attaching a secondprobe to a dorsal body surface of the human, the second probe having asecond accelerometer unit, and a second magnetic field unit; providing asignal processor coupled to the ultrasonic transducer, the first andsecond accelerometer units, and the first and second magnetic fieldunits; transmitting, from the ultrasonic transducer in the first probe,an ultrasound beam into an internal structure inside the body of thehuman; receiving, at the ultrasonic transducer in the first probe,ultrasound echo signals from the internal structure; generating, by thesecond magnetic field unit, a magnetic field transmitted to and detectedby the first magnetic field unit; calculating, using the signalprocessor, an orientation of the first accelerometer unit relative to afixed coordinate frame using derived parameters from the firstaccelerometer unit, and further calculating the derived parameters asunit vectors representing an orientation of the ultrasound beam and anorientation of the first magnetic field unit; calculating, using thesignal processor, an orientation of the second accelerometer unitrelative to the fixed coordinate frame using further derived parameters,and calculating the further derived parameters including body backsupport tilt angle (α) and unit vectors representative of a spatialdirection from the second magnetic field unit to the first magneticfield unit, an orientation of the second magnetic field unit, and anexpected direction of motion of the internal structure duringexhalation; calculating, using the signal processor, any varyingdistance between the first and second magnetic field units based on thedetection of the magnetic field; and processing, using the signalprocessor, results from the calculated orientations of the first andsecond accelerometer units, and the further derived parameters from thefirst and second accelerometer units, and the varying distance measuredby the first and second magnetic field units to generate correctionparameters to compensate for measurement errors in the receivedultrasound echo signals caused by motion of the ultrasonic transducer.2. The method of claim 1, wherein the generating correction parameterscomprises: decomposing a vector representing the distance between thefirst magnetic field unit and the second magnetic field unit along thedirection of the ultrasound beam; differentiating in time the decomposedvector representing the distance to yield incremental motion values;adding the incremental motion values to incremental Doppler effectmotion values as detected by use of the ultrasound echo signals from theinternal structure in at least a same time interval; correcting theadded incremental and Doppler effect motion values for an instantaneouscosine value of an angle between the ultrasound beam and a direction ofmotion of the internal structure; and summing the corrected and addedincremental and Doppler effect motion values to obtain internalstructure position variations describing corrected respiratoryparameters.
 3. The method of claim 2, wherein continuous variations inbeam orientation, bed angle, and abdominal surface motion are subjectedto the compensation.
 4. The method of claim 3, wherein the compensationassumes that an abdominal surface of the human moves in a directionperpendicular to a surface on which the human rests.
 5. The method ofclaim 2, further comprising: computing the angle between the ultrasoundbeam and a direction of motion of the internal structure for each motionincrement instead of assuming that the angle has a stationary value. 6.The method of claim 5, wherein the internal structure is one of a liver,spleen, or kidney of the human.
 7. The method of claim 1, wherein theinternal structure is one of a liver, spleen, or kidney of the human. 8.The method of claim 1, wherein the signal processor is configured tocalculate, based on inputs from the first and second accelerometer unitsand from the first magnetic field unit interacting with the secondmagnetic field unit, movement and orientation of an abdominal wall ofthe human in relation to the expected direction of motion of theinternal structure, the movement and orientation of the abdominal wallbeing related to respiration parameters associated with abdominalmuscles of the human.
 9. The method of claim 1, wherein the motion ofthe internal structure is a function of thoracic diaphragm movement inthe body of the human.
 10. The method of claim 1, wherein continuousvariations in beam orientation, bed angle, and abdominal surface motionare subjected to the compensation.
 11. The method of claim 10, whereinthe compensation assumes that an abdominal surface of the human moves ina direction (v_(mm)) perpendicular to a surface on which the humanrests.
 12. The method of claim 11, wherein the first and secondaccelerometer units comprise 3-axis accelerometer units.
 13. The methodof claim 12, further comprising: measuring, using the secondaccelerometer unit of the second probe, the tilt angle of a bed surfaceon which the human rests, assuming that the internal structure movesalong a same direction as the bed surface.
 14. The method of claim 12,further comprising: computing an angle between the ultrasound beam and adirection of motion of the internal structure for each motion incrementinstead of assuming that the angle has a stationary value.
 15. Themethod of claim 1, further comprising: measuring tilt based on adirection of gravity using the first and second accelerometer units,wherein the first and second accelerometer units comprise 3-axisaccelerometer units; and measuring up and down motion of the first probeusing the first magnetic field unit with assistance of the magneticfield emitted by the second magnetic field unit, wherein the measuredtilt and measured up and down motion are used to compensate for themeasurement errors.
 16. The method of claim 15, further comprising:measuring, using the second accelerometer unit of the second probe, thetilt angle of a bed surface on which the human rests, assuming that theinternal structure moves along a same direction as the bed surface. 17.The method of claim 15, further comprising: computing an angle betweenthe ultrasound beam and a direction of motion of the internal structurefor each motion increment instead of assuming that the angle has astationary value.
 18. The method of claim 1, further comprising:measuring, using the second accelerometer unit of the second probe, thetilt angle of a bed surface on which the human rests, assuming that theinternal structure moves along a same direction as the bed surface. 19.The method of claim 1, further comprising: computing an angle betweenthe ultrasound beam and a direction of motion of the internal structurefor each motion increment instead of assuming that the angle has astationary value.
 20. The method of claim 19, wherein the internalstructure is one of a liver, spleen, or kidney of the human.